To continuously measure or monitor the liquid or fluid contents of a large receptacle such as a tank, a marine or automotive tanker, the level sensing mechanism should not be adversely affected by the liquid. Further, in the instance of cargo carriers, the liquid carried is not always uniform between trips. A marine tanker for example might in the same tank carry crude products or ballast water on sequential trips.
To assure that the liquid gauging mechanisms or system remains operable under all circumstances, the system should be segregated from the liquid as much as possible. However, to maintain overall accuracy, it must nonetheless be capable of sensing or monitoring even minute changes in liquid level.
In the present arrangement, the liquid level gauging means comprises in brief, a pressure sensing chamber which is normally disposed at or near the floor of a vessel or tank. The pressure sensing chamber is communicated with a source of a pressurizing fluid such as air or preferably an inert gas.
At least one portion of said pressure sensing chamber is provided with a flexible or partially displaceable diaphragm. The diaphragm is of sufficient expanse that it will deflect from a normal neutral position in response to a pressure which is applied to either side of the diaphragm.
The pressurizing medium will in effect serve to neutralize deflection of the diaphragm while the gauge is in operation. A switching means within said pressure sensing chamber is actuated in response to displacement of the diaphragm either inwardly or outwardly. However, the flow of pressurizing medium which is controlled by pressure control means, is so regulated to maintain the diaphragm in its neutral position.
The pressure thereby maintained within the pressure sensing chamber is indicative of the static pressure on the external side of the diaphragm due to liquid in the tank, and consequently is indicative of the height of the contained liquid.
It is therefore an object of the invention to provide an accurate monitoring system for a liquid holding tank. A further object is to provide a liquid level monitoring system, having a wide operating range, and which has minimum exposure to the liquid being measured.